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function crc8(data, length)

{

/*

CRC calculation

http://ghsi.de/CRC/index.php?Polynom=100110001&Message=4F90CB2E

with polynomial 100110001

*/

    var crc = 0;

    for (var i=length-1; i>=0; i--)

    {

        var doInv = (((data>>i)&1) ^ (crc>>7)&1);

        crc=(crc<<1)&0xff;

        crc=crc|doInv;

        crc=crc^((doInv<<4)|((doInv<<5)));

    }

    return crc;

}

function rshift(num, bits) {

    num = num - (num % Math.pow(2,bits));

    return num / Math.pow(2,bits);